7-Pin S (ISO 3731)

Definition: 7-Pole S (ISO 3731)

What does a 7-pin S plug do?

More and more vehicles can be found on the public roads every day. It is getting busier and busier because of all the cars, but also because of the lorries and trailers. For traffic safety, it is extremely important that all vehicles are well lit. Trucks are fitted with working lights as standard, but trailers are not. These have to be connected to the lorry so that an electrical connection can be made. This connection is established by means of a 7-pin S and 7-pin N plug. These plugs are specially made for the truck and trailer sector and do not fit other vehicles such as trailers. There, the normal 7-pin connectors are being used.

Different ways of connecting

As mentioned earlier, an electrical connection must be established between a truck and trailer. In this way, the trailer will receive electricity which will enable the lighting to be operated. This can be achieved in two different ways. Firstly, the 7-pin S and 7-pin N plugs can be used. These must be connected both to the truck and to the trailer. If only one plug is used, not all the lighting will be powered. As a second method of connection, you can use a 15-pin connector (ISO 12098). In this way, no two cables are needed, just like the 7-pin plugs, but it goes through 1 connection.

Difference between 7-pin S and 7-pin N connection

A 7-pin N and S plug both supply a trailer with electricity for its lighting. The purpose of the plugs is the same, to make the connection between the truck and the trailer, but the result is different. The plugs both supply half of the total lighting on the trailer. So together they ensure that all the lighting works. To create a clear picture, the diagram below was created. It is easy to see which plug provides which lighting.

7-pin N 

  1. Mass
  2. Rear, contour, width and license plate light left
  3. Indicator left side
  4. Brake lights
  5. Indicator right side
  6. Rear, contour, width and license plate light right
  7. Checking the trailer brake

7-pin S

  1. Mass
  2. Not allocated
  3. Reversing light
  4. Constant power supply (+24V)
  5. Control for mass
  6. Power switch
  7. Rear fog lamp

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